1. Field of the Invention
The present invention is directed to a detachable filtration device for use with a respirator, wherein the filtration device has a rigid frame structure that enhances overall performance and use of the respirator.
2. Description of Related Art
Respirators are commonly employed to filter the air inhaled by a user under hazardous breathing conditions such as in environments having noxious vapors or particulates suspended in the air. A conventional respirator includes a face mask which covers the nose and mouth of the user. This face mask has one or more inlet valves through which air is drawn as the user inhales, and an outlet valve through which air exits the face mask as the user exhales. A filtration device is connected (either integrally or detachably) over the inlet valve so as to form a closed air channel between the filtration device and the interior of the face mask. In this manner, air is first drawn through the filtration element and filtered as the user inhales.
A key consideration in designing respirator filtration devices is filtering efficiency. The filtration device must be capable of removing a sufficient amount of contaminants from the air so as to supply "safe" breathing air to the user as prescribed by applicable statutes and regulations. Enhanced filtering efficiency is often obtained by utilizing highly efficient filter materials such as a tightly webbed or woven materials and to use multiple layers of the filter material. However, by using these tightly webbed and multiple layers of material, the effort required by the user to draw a sufficient volume of air through the material (also known as breathing resistance) is likewise increased.
Thus, a competing interest or consideration in designing filtration devices has been to reduce the amount of breathing resistance provided by the filtration device. Breathing resistance has been quantified as the pressure drop across the filtration element--the larger the difference in pressure between the air outside the filter and the air inside the filter at a given volumetric flow rate, the greater the breathing resistance experienced by the user.
In order to reduce this pressure drop, more recent designs have attempted to increase the overall filtration surface area of the device. This has been accomplished by providing a device comprised of two filter pads secured along their outer edges to face opposing directions. (See, e.g., U.S. Pat. No. Re. 35,062). The filter pads are separated by spacers or a baffle to form an interior region in which the air may be drawn through the filters. A breather tube is provided through one of the pads to connect this interior region with the inlet valve of the respirator face mask. As the user inhales, air is drawn through the surfaces of both filter pads into the interior region then drawn through the breather tube into the face mask via the inlet valve.
While this prior art design is useful in reducing breathing resistance without significantly detracting from filtration efficiency, a need remains in the art to develop even better designs having improve performance and use characteristics. For instance, the filtration device is generally secured to and disconnected from the respirator face mask by connecting the breather tube to the respirator using a threaded or bayonet type fitting. In doing so, the user must grasp and touch the filter pads and twist or otherwise manipulate the device to make the connection. This means that any soil on the user's hands can contaminate the filter pads, potentially blocking a portion of the available filtration surface area and reducing filtration efficiency in use. In disconnecting a spent device from the respirator, the user's hands may come into contact with potentially harmful material deposited on the used filter pads. Handling the filters may also cause particles on the pads to flake off and/or become airborne so as to present harm to a bystander or to the user who has removed his or her respirator while replacing the filtration device.
In twisting or otherwise manipulating the device for connection or disconnection with the respirator face mask, the pliable filter material tends to be rotated or turned further than the relatively stiff breather tube being connected, thereby placing stress on the filter material surrounding the breather tube. This relative rotational stress on the filter material can potentially lead to tearing or other damage of the material and possibly even separation of the filter material from the breather tube.
Thus, preventing user contact with the filter material, bending of the filter material during removal and attachment, and relative rotation between the filtration material and the breather tube are desirable objectives to enhance the overall performance and use of the filtration device. Of course, it is likewise an important objective to maintain filtration efficiency while reducing breathing resistance, and to increase the overall filtering surface area while making the filtration element relatively compact so as not to obstruct the user's view or otherwise frustrate the user's ability to work when wearing the respirator.